The emails, which were revealed during a witness session with James Murdoch at the inquiry, triggered demands for the resignation of Mr Hunt, but the media secretary won the support of the prime minister.

Mr Hunt is set to give evidence later, but unconvincing testimony from the two men next week could further damage his reputation.

Earlier this week, Lord Leveson warned off Commons Speaker John Bercow from allowing Labour to pursue the matter in the Commons. Shadow media secretary Harriet Harman saidthe opposition would pause its moves at a parliamentary level until the three men – Mr Hunt included – had given evidence at Leveson.

Mr Michel and Mr Adam's testimony will be the first part of what is effectively a political trial for Mr Hunt, whose professional survival depends on what is said at the inquiry.

It is also an extremely sensitive moment for the prime minister, who has gone out on a limb defending his media secretary and whose judgement will be questioned if he is eventually forced to sack him.

Also set to give evidence next week are Lord Mandelson, who was one of the key architects of New Labour's spin operation, Tom Watson, who doggedly pursued the phone-hacking story with the Guardian newspaper, and Tessa Jowell, whose phone was hacked while she was media secretary.

Jeremy Paxman and Andrew Marr will also be giving evidence in what will be a colourful week at the inquiry.